Robert Lewandowski has vowed to give Borussia Dortmund everything he has until his controversial summer switch to their rivals Bayern Munich.

Poland striker Lewandowski signed a five-year deal with the German, European and world champions on Saturday which starts in the summer once his current deal with Dortmund expires.

Though the transfer – hot on the heels of Mario Goetze’s move from Signal Iduna Park to the Allianz Arena – has left many Dortmund supporters deflated that such defections will prevent them from ever remaining comparable to the Bavarians, the 25-year-old issued a club statement to the BVB website on Sunday.

Lewandowski said: “BVB fans, I would like now to briefly turn to you.

“We still have half a year in which we have some goals that we want to achieve together.

“Although there are some fans of you who do not agree with my decision, I hope for your support!

“Anyway, I'll give everything for BVB!”

Dortmund remain in Champions League contention with the knockout phase beginning next month. They begin with a last-16 tie against Zenit St. Petersburg.

They look extremely likely to be out of the league title hunt well before the business end of the season for a second straight year, however: leaders Bayern are 12 points clear of fourth-placed Dortmund and have a game in hand.